Graphic recorders are known to the prior art. Typically, such recorders employ a pen or other similar recording element which is movable relative to a moving recording medium, the combined movement of the recording element and medium being controlled to produce a desired representation.
The use of multiple pens for such purposes as multi-color plotting are known to the prior art. An example of such a system is disclosed in U.S. Pat. No. 3,401,401 issued Sept. 10, 1968, to Read et al for MULTIPLE PEN PLOTTER CARTRIDGE, which is hereby incorporated by reference. The disclosed Read embodiment employs four pens which may be independently selected for color selection, for example. However, the selection of each pen requires the activation of a different pen actuating device. Thus, the movable support for the pens must also support and move an independent actuating device for each pen. The overall mass of the moving support contributed by the multiple pens and independent actuating elements has placed a practical limit of four pens on this technique.
An attempt to overcome the mass problems of multiple pen graphic recorders is disclosed in U.S. Pat. No. 4,135,245 issued Jan. 16, 1979, to Kemplin et al for PLOTTER WITH AUTOMATIC PEN-CHANGER, which is hereby incorporated by reference. The Kemplin system, like similar prior art systems, employs a pen repository, at which multiple pens are maintained, and a single pen recording head. The pen which is immediately desired for recording purposes is retrieved from the repository after which the recording operation is initiated. When a pen change is desired, the recording operation stops and the recording head returns the pen it has utilized to the repository where it also retrieves an alternative pen, according to instructions. While this does reduce the mass of the recording head by the mass of those pens not in use, together with associated actuating and supporting structures, it increases the recording time by the amount of time necessary to return a previously utilized pen and to retrieve a pen that it is desired to use.
Systems meeting the general description of the two systems described above are in common use. Since such systems are typically numerically controlled, each has qualities which frustrate the capabilities of the control systems. For example, heavier masses require heavier mechanisms for moving that mass which may lead to difficulties in acceleration speed as well as precision. Greater time requirements (i.e., the pen retrieval, for example) introduce a delay not required by the control system.